Illumination systems often include a source that provides a beam of light with circular symmetry, such as a halogen, metal halide, or xenon lamp with a parabolic or elliptical reflector, or gas or solid-state lasers. Such illumination systems also often deliver illumination to targets wherein the targets benefit from the delivered illumination having the shape of a line, equivalently termed a slit, or a shape provided by an optical transformation of a line such as by a lens or mirror. Hence a conversion of the shape of the illumination from the input circle shape to the output line shape is necessary to achieve such illumination systems.
Although illumination shape conversion may be achieved by arrangements of discrete optical elements that convert the shape in free space, it is often desirable to use a shape-converting fiber optic cable for delivery of the illumination, such as in cases where the target is relatively remote or not conveniently accessible from the source. For example, U.S. Pat. No. 3,933,556 to Strack describes a fiber optic image transporting device for converting the shape of optical images, including line-like and ring-like configurations. In some cases it is advantageous to use a shape-converting fiber optic cable with a single input and a plurality of outputs. Circle-to-line fiber optic cables, equivalently termed line-to-circle fiber optic cables, for example Dolan-Jenner QF and QDF type cables with single and dual outputs, respectively, are commercially available solutions for such illumination systems.
In some cases the individual optical fibers within shape-converting fiber optic cables are substantially spatially indistinguishable, such as due to randomization within the cable or to homogeneity of the source light incident upon the input. For example, U.S. Pat. No. 4,190,347 to Siegmund describes a line illuminator for a line-scanning document copier including a fan-shaped array of optical fibers with light-output ends juxtapositioned along a line, and opposite light-receiving ends tightly bundled together. In cases where the individual optical fibers are substantially spatially indistinguishable, the delivered illumination pattern is intrinsically fixed and can only vary by extrinsic mechanical adjustments of either the cable output or intermediary optical elements, such as lenses and/or mirrors, between the cable output and the illumination target.
Various configurations are known in the art wherein the individual optical fibers within shape-converting fiber optic cables are juxtapositioned in an orderly fashion such that they are spatially distinguishable. For example, U.S. Pat. No. 3,191,487 to Kruythoff et al. describes a system for optical image transmission in which from each point of the object of which an image is to be transmitted a colored beam of light is derived whose spectral composition is representative for the position of the image point in the image and wherein the colored light beams are combined and transmitted to an image space in which they are separated so as to form the image. Also, U.S. Pat. No. 5,671,084 to Kurtz describes a fiber optic circle-to-line converter where the fibers would be randomized, or reorganized in a structured way, such that at the output end, there is a line of light with a much more uniform profile than the input light. In cases where the individual optical fibers are spatially distinguishable, the delivered illumination pattern is not intrinsically fixed but instead may be variable by varying the spatial and/or angular content of the illumination pattern incident upon the input of the fiber optic cable.
It may be desirable for an illumination system to provide adjustable concentration of the delivered light into smaller target areas. For example, in a bright-field or fluorescence imaging (or video) system with variable magnification, it may be desirable to concentrate or condense the illumination light to correspond to larger magnification, i.e., smaller field of view, so as to reduce the exposure time (or increase the frame rate) necessary to capture an image (or video) of sufficient brightness. Alternatively, in a bright-field or fluorescence imaging (or video) system wherein the target size is variable, it is often desirable to concentrate or condense the illumination light to correspond to smaller target sizes so as to reduce the exposure time (or increase the frame rate) necessary to capture an image (or video) of sufficient brightness. Arrangements of discrete optical elements, such as variable beam contractors, are well-known in the art to provide variable concentration of illumination. However, in cases where the target is relatively remote or not conveniently accessible with respect to the illumination source so that a fiber optic cable is desired for delivery of the illumination to the target, adjustable concentration or condensation of the delivered light into smaller target areas requires adjustment of the illumination delivery path with respect to the target. For example, the output of the fiber optic cable may be adjustably positioned closer to the target; however, mechanical adjustment of the output of a fiber optic cable in a relatively remote or not conveniently accessible location is often undesirable due to complexity, space constraints, and cost.